linux-kernel - Re: [PATCH] x86/numa: move setting parse numa node to num_add

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Message-ID: <20171129130158.hji24remijkaoydb@dhcp22.suse.cz>
Date:   Wed, 29 Nov 2017 14:01:58 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     zhong jiang <zhongjiang@...wei.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, x86@...nel.org,
        lenb@...nel.org, akpm@...ux-foundation.org, vbabka@...e.cz,
        linux-mm@...ck.org, richard.weiyang@...il.com,
        pombredanne@...b.com, linux-kernel@...r.kernel.org,
        linux-acpi@...r.kernel.org
Subject: Re: [PATCH] x86/numa: move setting parse numa node to num_add_memblk

On Wed 29-11-17 20:41:25, zhong jiang wrote:
> On 2017/11/29 20:03, Michal Hocko wrote:
> > On Wed 29-11-17 17:13:27, zhong jiang wrote:
> >> Currently, Arm64 and x86 use the common code wehn parsing numa node
> >> in a acpi way. The arm64 will set the parsed node in numa_add_memblk,
> >> but the x86 is not set in that , then it will result in the repeatly
> >> setting. And the parsed node maybe is  unreasonable to the system.
> >>
> >> we would better not set it although it also still works. because the
> >> parsed node is unresonable. so we should skip related operate in this
> >> node. This patch just set node in various architecture individually.
> >> it is no functional change.
> > I really have hard time to understand what you try to say above. Could
> > you start by the problem description and then how you are addressing it?
>   I am so sorry for that.  I will make the issue clear.
>  
>   Arm64  get numa information through acpi.  The code flow is as follows.
> 
>   arm64_acpi_numa_init
>        acpi_parse_memory_affinity
>           acpi_numa_memory_affinity_init
>               numa_add_memblk(nid, start, end);      //it will set node to numa_nodes_parsed successfully.
>               node_set(node, numa_nodes_parsed);     // numa_add_memblk had set that.  it will repeat.
> 
>  the root cause is that X86 parse numa also  go through above code.  and  arch-related
>  numa_add_memblk  is not set the parsed node to numa_nodes_parsed.  it need
>  additional node_set(node, numa_parsed) to handle.  therefore,  the issue will be introduced.
> 

No it is not much more clear. I would have to go and re-study the whole
code flow to see what you mean here. So you could simply state what _the
issue_ is? How can user observe it and what are the consequences?

Sorry for my laziness, I could go and read the code but the primary
point of the changelog is to be _clear_ about the problem and the fix.
Call paths can help reviewers but the scope should be clear even without
them.
-- 
Michal Hocko
SUSE Labs